Many different fuel systems are utilized to introduce fuel into the combustion chambers of an engine. One type of fuel system is known as the common rail system. A typical common rail system utilizes one or more fuel filters to remove contaminants from the fuel and one or more pumping mechanisms to pressurize fuel and direct the pressurized fuel to a common manifold also known as the rail. Individual injectors draw pressurized fuel from the common rail and inject the fuel into the combustion chambers. In order to optimize operation of the engine, fuel pressure is controlled within a desired pressure range by controlling the pumping mechanisms. At times, however, pressure fluctuations or spikes may still occur. Without intervention, these pressure spikes could damage fuel system components and/or degrade fuel system performance.
One way to protect the fuel system from undesired pressure fluctuations and degraded system performance includes selectively relieving the system of fuel and/or air by way of one or more relief valves. An example of this protection method is disclosed in U.S. Pat. No. 7,343,901 (the '901 patent) issued to Mori et al., on Mar. 18, 2008. The '901 patent describes a common rail fuel system having a fuel filter located downstream of a feed pump to filter fuel drawn from a tank by the feed pump and discharged to a high pressure pump. Fuel from the high pressure pump is directed to at least one injector by way of a common rail. A relief valve is located on an outlet side of the feed pump and opens if the fuel pressure applied to the fuel filter exceeds a predetermined value. When the relief valve opens, a part of the fuel discharged by the feed pump is returned to the fuel tank. Thus, excessive fuel pressure can be prevented from acting on the fuel filter.
The relief valve of the '901 patent has a valve chamber, a ball valve, and a spring. The valve chamber is formed above an air collection chamber of the fuel filter. The ball valve is located within the valve chamber to open or close a communication hole that connects the valve chamber to the air collection chamber. The spring biases the ball valve in a valve-closing direction. Thus, when fuel pressure acting on the fuel filter exceeds the biasing force of the spring, the ball valve opens the communication hole. Accordingly the fuel pressure acting on the fuel filter is released through the relief valve, and the air collected within the air collection chamber of the fuel filter is bled away.
Although the relief valve of the '901 patent may sufficiently protect fuel system components by relieving excessive pressures, it may be problematic. In particular, a seat against which a ball of the ball valve seals must be manufactured to tight tolerances and often requires grinding and polishing processes. These tight tolerances and complicated manufacturing processes can significantly increase the cost of a system employing the ball valve. In addition, the opening and closing of the ball valve may create undesired pressure fluctuations within the system. Furthermore, the system must include an air collection chamber for periodic bleeding of air from the fuel filter. Still further, pressure pulses from the high pressure pump may not be adequately dampened.
The disclosed relief valve is directed to overcoming one or more of the problems set forth above.